1. Field of the Invention
This invention relates to an ion selective electrode pair for potentiometrically measuring ionic activity or ionic concentration of a specific ion in an aqueous liquid sample such as blood, urine, saliva or other body fluid, and also relates to a method of manufacturing an ion selective electrode pair.
2. Description of the Prior Art
In U.S. Pat. Nos. 4,053,381 and 4,214,968, Japanese Unexamined Patent Publication No. 57(1982)-17851 and Japanese Unexamined Patent Publication No. 58(1983)-156848 (GB 2121183 A), there is disclosed a planar film-like dry type ion selective electrode pair to be incorporated in an ionic activity measuring instrument for potentiometrically measuring ionic activity or concentration of a specific ion contained in aqueous liquid samples such as body fluid (e.g. blood including whole blood, serum and plasma; lymph; saliva; cerebrospinal fluid; vaginal liquid; urine), liquors, waste water, and stream water using a very small amount (sessile drop amount) of such samples.
The film-like ion selective electrode pair disclosed in Japanese Unexamined Patent Publication No. 58(1983)-156848 is especially epoch-making in that electrical insulation between a pair of ion selective electrodes can be easily established and accordingly the ionic activity measuring instrument using the ion selective electrode pair can be reduced in size.
The ion selective electrode pair, utilizing the fact that the ion selective layer of the ion selective electrode pair is substantially an insulator, is formed by providing a V-shaped groove on a metal conductive layer before superposing the ion selective layer by scribing with a sharp cutting edge having a wedge-shaped cross section, so that the metal conductive layer is divided into a pair of portions insulated from each other, each forming an electrode. With this arrangement, a very compact ion selective electrode pair can be easily produced. However, it is very difficult to completely remove metal cuttings produced by scribing from the V-shaped groove, and when the metal cuttings mingle in the upper layers, sufficient electrical insulation cannot be maintained, thereby producing a defective product. Further, since scribing is inherently an operation to push the metal layer aside, there arise various problems.
FIG. 7 is an enlarged fragmentary cross-sectional view showing the V-shaped groove. In FIG. 7, reference numeral 10 denotes an ion selective electrode pair. The ion selective electrode pair 10 is formed by laminating a silver layer 14, a silver halide layer 16 and an ion selective layer 18 in this order on an insulating base 12. Reference numeral 20 denotes a groove having a V-shaped cross section formed by scribing the silver layer 14 to divide it into a pair of insulated portions each forming an electrode. In order to obtain a good electrical insulation between the electrodes, the depth of the V-shaped groove 20 should reach the insulating base 12 through the silver layer 14, and thus, the portion of the silver layer 14 and the insulating base 12 forced aside by the cutting edge forms a raised portion 22 on each side of the V-shaped groove 20. This is disadvantageous in that, in order to cover the silver layer 14 at the raised portion 22, the thickness of the ion selective layer 18, which is of expensive material, must be increased so that the manufacturing cost of the ion selective electrode pair is increased. Further, when the ion selective electrode pair is incorporated in an ionic activity measuring instrument, the ion selective electrode pair cannot be brought into close contact with a mask on which is mounted a porous bridge and which covers the surface of the electrode pair except the portions on which sample liquid and reference liquid are deposited. Further, since the V-shaped groove 20 is formed deep into the insulating base 12, the insulating base 12 is apt to be deformed.